


Snippets from Mute!Cross AU.

by AshTheRat



Category: Undertale (Video Game)
Genre: Abuse, Angst, Betrayal, Branding, Hurt/Comfort, Implied/Referenced Rape/Non-con, Implied/Referenced Torture, M/M, Major Character Injury, Multi, Mute!Cross, Muteness, Post-Traumatic Stress Disorder - PTSD, Psychological Trauma, Self-Indulgent, Torture, Vomiting
Language: English
Status: Completed
Published: 2021-01-27
Updated: 2021-02-16
Packaged: 2021-03-12 14:00:28
Rating: Explicit
Warnings: Graphic Depictions Of Violence
Chapters: 2
Words: 1,653
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/29011659
Author URL: https://archiveofourown.org/users/AshTheRat/pseuds/AshTheRat
Summary: Traumatized after brutal punishments by Nightmare, Cross stops talking.Killer gets involved.(Random snippets from an AU idea that was spawned on twitter.)
Relationships: Sans/Sans (Undertale)
Comments: 9
Kudos: 116





	1. Chapter 1

**Author's Note:**

> Disjointed, mostly unfinished little snippets that needed a place to be posted. Extremely self-indulgent.

The door to Cross’ room is open.

That alone gives Killer pause. Cross isn’t in the habit of leaving the door open for curious snoopers to sniff around when he’s out, and he always closes it for the sake of privacy when he’s in. Killer had been hoping (pretending) today would be a good (less horrible) day, an easy day, ignoring the muffled screaming he’d heard from Nightmare’s room just a few hours earlier. 

Killer moves silently to the open doorway and peers inside. The lights are off, but through the dim light streaming in through the hallway he can see Cross’ broken form slumped in the corner between his bed and the wall. 

(Like he was callously tossed onto the floor, and was unable to even climb into his own bed.)

“Criss-Cross,” Killer prompts.

There’s no reaction. Killer exhales slowly through his nasal aperture and shuffles into the room, closing the door behind him. It’s only when he crouches down in front of Cross that he can see how bad he looks, blood staining his teeth and chin, spreading down to his neck and seeping into his turtleneck in dark, crusty splotches. His bones look sickly even in the dim light of the room, and there are cracks, cuts and bruises covering every single sliver of bare bone Killer can see.

Some small, loud part buried under the numbness of Killer’s target-shaped soul nudges him to say something, anything. An apology - for not talking Nightmare out of doing what he’s been doing to Cross. For not even trying. For standing quietly outside the room and listening to Cross’ blood-curdling screams and doing nothing about it. 

When Killer raises his hand to touch Cross’ bruised face, the other’s expression twists into something anguished and terrified, though he doesn’t flinch or move away. (He knows that’d just make it worse.) 

“It’s okay, it’s just me,” Killer soothes, keeping all of the snark and sarcasm out of his tone just this once. He’s not sure how aware Cross is of his presence as he begins to push gentle pulses of healing magic through his palm, but Cross’ tight expression seems to relax, just a little. 

Killer is a miserable healer due to his LV, and Nightmare will no doubt notice that he tried to undo some of the damage he so meticulously carved into Cross, but fuck it. Fuck all of it.

He’s done standing outside the room.


	2. The failed escape.

**Summary for the Chapter:**

> Killer has made a deal with Ink to rescue Cross. It goes terribly wrong.

They’re meant to be meeting Ink in the garden in fifteen minutes. Killer made sure to tell Cross to stay in his room without giving him too many details, just in case - but Cross’ room is empty. It’s fucking _empty._

Killer doesn’t usually lose his cool. Most situations can be dealt with with a grin and a sharp knife, but there is only one reason why Cross wouldn’t be in his room when Killer specifically asked him to be. (He follows orders very well these days. Mechanically, with empty eyes, he goes wherever he’s told, and kills whoever he’s told, never uttering a single word.) 

The timing couldn’t possibly be worse. Of all the fucking days of the week, of all the fucking seconds in a day-

Killer barges through the door to Nightmare’s bedroom, without a plan. Without a thought. 

His LV flares at the sight before him, his target-shaped soul distorting painfully at the smell of burning bone and marrow, the promise of wonderful, beautiful violence.

Cross is flat on his back on the floor, head wrenched back and spine arching painfully off the floor, his entire body spasming violently against the oily tentacles holding him down. Nightmare is on top of him, pressing a red-hot branding iron firmly against Cross’ exposed sternum. The bone hisses and sizzles, a small cloud of thick white smoke rising from where the metal touches it.

Cross isn’t screaming, his voice locked away even as he’s going through pain that must be unbearable, expression twisted in agony as tears stream ceaselessly down his sweaty face. Maybe he simply can’t anymore, or maybe Nightmare’s meticulous torture has finally conditioned him to stay silent at any cost.

Nightmare pulls the branding iron away from Cross’ sternum and leans forward to inspect his work. 

“Hello, Killer,” Nightmare greets him, placing the iron back into the fireplace. Cross has gone limp and mostly still, trembling weakly as his ribcage rises and falls, breath coming in short, fast gasps. “Did you need something? As you can see, I’m a little preoccupied.”

“Heh, so I see,” Killer says, casually slipping his hands into his pockets to hide the way they clench into fists, “what’d he do now? Caught him singing?”

“Oh no, he doesn’t do that anymore,” Nightmare croons, stroking Cross gently, almost affectionately, over the skull, “I just figured he might need a reminder.”

Nightmare smiles pleasantly up at Killer, and Killer immediately knows that he knows. Knows about the times Killer has healed Cross’ numerous wounds and undone Nightmare’s hard work. Knows about secret meetings in the gardens and of dangerous, dangerous games.

“Ah, but you were wanting to join me, weren’t you?” Nightmare continues, “You have your own bone to pick with him, after all.”

There is absolutely no way Killer can say no. Not if he wants himself and Cross to survive this.

“Yeah, sounds like a good time,” Killer says with a grin, and is almost surprised by how casual he sounds.

“The iron should be hot enough again by now,” Nightmare muses as Killer moves closer, turning toward the fireplace where the iron glows pretty and red, like a little blood moon. 

Killer crouches down next to Cross and studies him, keeping his grin wide and unreadable. The half-moon shaped wound on Cross’ sternum is blackish-red, weeping fluids and marrow as the surrounding bone darkens with infection. The iron has scorched right through the thin, sensitive periosteum and started gouging deep into the dense bone beneath. Nightmare must have branded the same spot several times for it to look so bad. Similar scars, burns and half-healed wounds litter every inch of visible bone that Killer can see through Cross’ open coat, and Killer guesses the rest of the ex-guard’s body must look the same.

“So is there a trick to this?” Killer asks, stalling, as Nightmare offers him the newly heated iron.

“Press the iron down where I’ve already set down an example,” Nightmare says patiently. “Be careful about it, don’t mess up the mark. I want the edges nice and crisp.”

“Sure, nice and crisp,” Killer echoes. 

The sound of Killer’s familiar voice causes Cross to finally open his sockets, blurry eyelights flitting aimlessly around for a second before focusing on his face. At the sight of Killer, Cross’ expression melts into one of desperate relief. He probably thinks he’s saved, that somehow Killer can fix this. Killer is Nightmare’s right hand man, his favorite - if anyone can stop this, it’s him.

Then he sees the iron in Killer’s hand.

Thoughts slowed by pain and shock, Cross stares at the iron with a look of confused betrayal on his face. Killer doesn’t let it linger for too long, doesn’t want it to fester and grow too large -- and presses the branding iron down against Cross’ sternum.

Cross tries to double over, but Nightmare’s tentacles press him flat against the floor. Killer isn’t sure if he imagines it, or if he can really feel the way the iron burns through layers of spongy bone and sinks deeper, the edges sizzling and cauterizing the wound. Somehow, Cross still doesn’t scream, but his sockets have gone wide and empty, and he’s clenching his teeth so hard that Killer can almost hear them crumbling under the pressure. Sweat runs in heavy beads down his face, and at some point he must’ve bit his tongue, as blood and saliva drips through his teeth and down his chin.

“And hold it there…” Nightmare murmurs into Killer’s acoustic meatus, a tentacle coiling gently around Killer’s wrist as if to encourage him to increase the pressure.

Killer feels the way Cross struggles beneath him, squirming desperately in Nightmare’s powerful grip. The fingers of Cross’ right hand straighten jerkily, before his index, middle and ring fingers curl shakily back against his palm. Cross can’t raise his hand to his face, but Killer recognizes the sign anyway. They’ve practiced it together several times, during the quiet hours after a successful mission.

_Why,_ Cross signs. 

“Careful, you’re starting to ruin the edges now,” Nightmare warns, and Killer pulls the iron away, perhaps a little too quickly to seem unaffected. He’s sweating, his soul flickering wildly where it hovers in front of his ribcage.

Cross turns his head to the side and vomits, raw magic spilling down his chin and the side of his face. Nightmare makes a disgusted noise, tentacles retreating from around Cross to avoid the mess.

“Disgusting,” he spits callously, before he stands up and primly straightens his bloodstained clothes. Suddenly, Cross seems to be of no interest to him, like he’s a toy that’s been played with too roughly, and then abandoned once nicks show up in its paint. 

“Since you’re here, you can clean up this mess,” Nightmare tells Killer. Then, smugly, he adds: “You’re the one who caused it, after all.”

“Heh, sorry ‘bout that, boss,” Killer hears himself say, his voice sounding hollow and flat in his head. Part of him wants to laugh, because it’s fucking hilarious, isn’t it? Somehow he’s managed to betray two people he cares about in a single day, while also trying to protect them both. It’s a new achievement for him. 

He blinks, and feels the black, sticky tears crawl slowly down his cheeks.

Nightmare fails to hide his expression of glee, looking almost drunk on the misery that he’s absorbing from the two monsters in the room. Then, he steps through a portal and is gone.

**Notes for the Chapter:**

> There's meant to be a scene with Ink taking place before this, but my writing brain is a chaotic unpredictable gremlin and has decided that we write and post this now right now.
> 
> Tags for this chapter: Torture, branding, betrayal, vomiting.


End file.
